In Yeast, the 3′ Untranslated Region or the Presequence of ATM1 Is Required for the Exclusive Localization of Its mRNA to the Vicinity of Mitochondria

Abstract

We isolated mitochondria from Saccharomyces cerevisiaeto selectively study polysomes bound to the mitochondrial surface. The distribution of several mRNAs coding for mitochondrial proteins was examined in free and mitochondrion-bound polysomes. Some mRNAs exclusively localize to mitochondrion-bound polysomes, such as the ones coding for Atm1p, Cox10p, Tim44p, Atp2p, and Cot1p. In contrast, mRNAs encoding Cox6p, Cox5a, Aac1p, and Mir1p are found enriched in free cytoplasmic polysome fractions. Aac1p and Mir1p are transporters that lack cleavable presequences. Sequences required for mRNA asymmetric subcellular distribution were determined by analyzing the localization of reporter mRNAs containing the presequence coding region and/or the 3′-untranslated region (3′UTR) of ATM1, a gene encoding an ABC transporter of the mitochondrial inner membrane. Biochemical analyses of mitochondrion-bound polysomes and direct visualization of RNA localization in living yeast cells allowed us to demonstrate that either the presequence coding region or the 3′UTR of ATM1 is sufficient to allow the reporter mRNA to localize to the vicinity of the mitochondrion, independently of its translation. These data demonstrate that mRNA localization is one of the mechanisms used, in yeast, for segregating mitochondrial proteins.

ACKNOWLEDGMENTS

We thank A. Delahodde, E. Carvajal, and M. G. Claros for useful discussions and comments on the manuscript. We thank D. Beach and K. Bloom for the kind gift of plasmids required for the RNA-labeling system. We are also grateful to D. Ojcius for proofreading the manuscript.

This study was supported by funds from the CNRS (UMR 8541), the Ecole Normale Supérieure, the AFM (grant 586073), and the French Association Against Cancer (ARC grant 5691).